A seatbelt apparatus is an example of a vehicle occupant restraint apparatus. In a commonly used seatbelt apparatus, an occupant sitting in the seat is restrained by a seatbelt when the vehicle has collided or when a collision is anticipated.
Recently, tests have been conducted in an attempt to have seatbelt apparatuses operate when various other conditions are met aside from a vehicle collision. For example, JP 2004-74957 A discloses a technique wherein the force for restraining the occupant with the seatbelt is increased when the driver performs an emergency maneuver by suddenly applying the brakes or turning the steering wheel.
In the technique disclosed in JP 2004-74957 A, it is determined that the driver has performed an emergency maneuver and the tension in the seatbelt is increased when three conditions are met. These three conditions are that the vehicle speed be equal to or greater than a specific value, that the operating member operated by the driver be operated in an amount equal to or greater than a specific value, and that the speed with which the operating member is operated be equal to or greater than a specific value.
A summary of the vehicle occupant restraint apparatus disclosed in JP 2004-74957 A is described hereinbelow with reference to FIG. 11 hereof. A conventional vehicle occupant restraint apparatus 200 is composed of a vehicle speed sensor 201 for sensing the vehicle speed, a stroke sensor 203 for sensing the depression stroke of a brake pedal 202, a master cylinder 204 for increasing master cylinder pressure (braking hydraulic pressure) in accordance with the depression force of the brake pedal 202, a hydraulic pressure sensor 205 for sensing the master cylinder pressure, and a seatbelt apparatus 206. A wheel cylinder 209 is driven by the master cylinder pressure.
The seatbelt apparatus 206 is composed of a motor 207 for windably driving the seatbelt, and a seatbelt control device 208 for controlling the motor 207.
The seatbelt control device 208 controls the motor 207 to increase the tension in the seatbelt when a determination is made that three conditions are met. The first condition is that the vehicle speed be equal to or greater than a specific value, the second condition is that the master cylinder pressure be equal to or greater than a specific value, and the third condition is that the rate of change (differential over time) in the master cylinder pressure be equal to or greater than a specific value.
The vehicle occupant restraint apparatus disclosed in JP 2004-74957 A exemplifies a modification in which the second and third conditions are modified in the following manner.
The second and third conditions of a first modification are as follows. The second condition of the first modification is that the depression stroke be equal to or greater than a specific value. The third condition of the first modification is that the rate of change (differential over time) of the depression stroke be equal to or greater than a specific value.
The second and third conditions of a second modification are as follows. The second condition of the second modification is that the steering angle of the steering wheel (not shown) be equal to or greater than a specific value. The third condition of the second modification is that the rate of change of the steering angle (steering angle speed) be equal to or greater than a specific value.
The following is a description of a case in which the techniques of the second modification are employed in a vehicle occupant restraint apparatus. The following two possibilities are examples of sudden steering (act of rapid and extensive steering) of the steering wheel by the driver. The first steering is regular sudden steering, which the driver intentionally and appropriately makes a determination to perform. The second steering is erratic steering, wherein the driver has panicked (is in a state of mental confusion).
As described above, the seatbelt control device 208 according to the second modification determines, on the basis of the three primary factors of vehicle speed, steering angle, and steering angle speed, whether the driver has performed an emergency maneuver while the vehicle is moving. However, it is difficult to appropriately and quickly conclude based on this determination alone whether the steering is first steering or second steering. The reason for this is that the steering angle and steering angle speed may temporarily increase even when the driver is using first steering.
For example, when the vehicle is turning, the steering angle and steering angle speed may temporarily increase when the driver steers in a comparatively slightly unstable manner (the steering wheel fluctuates to the left and right).
Also, when the vehicle is moving at a comparatively low speed, the steering angle and steering angle speed may temporarily increase when the driver makes a quick turn (including making a U-turn, reversing direction, and continually turning).
In the case of first steering, the steering angle and steering angle speed return to their original appropriate values in a short amount of time (return to normal in a short amount of time) despite having temporarily increased. In other words, the steering angle and steering angle speed return to their original appropriate values even through they have exceeded the determination reference values in the second and third conditions as a result abrupt steering by the driver. The seatbelt control device 208 of the second modification ends up making a hypersensitive determination in the case of first steering. Therefore, there is room for improvement in terms of being able to appropriately and quickly determining whether the occupant needs to be restrained.
In view of this, there is a need for a technique whereby it is possible to more appropriately and more quickly determine whether the occupant needs to be restrained in cases in which the driver suddenly turns the steering wheel.